What's this Clam? / Is this a Gorilla Crab?

[Petrichor]

Greetings all! I need help identifying these two creatures, please.

First one (top left) I believe to be a clam of some sort. When I shine a light on it it'll shoot back into the rock then very slowly come back out. It looks to have a mantle of some sort because the middle looks more "fleshy" than the outer parts. There's also a bit of "hair" on top of it. It moved backwards into the rock so quickly I'm kinda hesitant to call it a clam since I'm not sure if clams can retract into a space that fast. I don't have a lot of experience with bivalves in general and don't know if they can move their shells in this manner.

The other three pictures are of a mystery crab I've had in my tank for a long time. He's now at a size that I'm able to see him more clearly and recognize that he might be a gorilla crab. First pic (top right, then going clockwise) is his head/body and parts of the leg (striped black and yellow with smaller white stripes), then part of his arm/claw (kind of a very dark blue/black with lighter blueish spots), and then the claw itself (tan on the "arm" then black at the pincers and fading to a brown/tan at the tip).

I assume it's a gorilla crab, or at least a bad crab of some sort, because of the pointed claw (looks similar to my emerald crabs claw in terms of shape), slightly hairy, striped legs, and black body. I did not see red eyes though, and tonight when I got the first two pictures he was scrapping at the rock work so I'm hoping he's just some sort of mithrax crab (I doubt it).

I also would like to know if anyone has any better crab trap ideas other than a glass cup with food at the bottom? I've tried to catch him that way, and all I get are hermit crabs. I am planning on rearranging my tank sometime before Christmas so I'll have a chance to nab him that way; would that be best? Thanks for any and all help!

Also sorry for my dirty glass. Part of the reason we're rearranging the tank is to be able to clean the glass better!

EDIT: I should mention I've checked Chuck's Hitchhikers Guide and didn't find anything that screamed a match at me for the crab.

 

[Sniperhank]

When it comes to crabs, I say remove when in doubt. Tilt a tall glass against the rock with some food in it. You'll have him by morning.

In terms of a clam, not sure what you are trying to point out.

 

[mr_X]

That's not a gorilla crab. I would say not to remove it unless you see ill effects from it. It's a marine creature just like all the rest. You are trying to keep a marine reef, and crabs are part of the reef.

 

[Petrichor]

It's good to know that it's not a gorilla crab. I'm still going to try to catch it so I can try and get a positive ID on it with some better pictures, but it's nice to know that it's not an immediate threat.

As for the clam I circled it in the image. You can see the scalloped edge of it's shell and the mantle (of that's what it is) underneath. I'm not sure what the "hairs" on top of it are. It's at an angle pointing to the bottom left of the picture.

 

[Sniperhank]

That doesn't look like a clam. It looks almost feathery to me...is that just reflection?

 

[mr_X]

It is a mollusk, but I don't know the exact name. I see them from time to time attached to rock.

 

[Petrichor]

I assume it must've been there since I started the tank. Should I leave it where it is or move it to more optimal conditions, and where would that be? I have a royal gramma, yellow-tailed damsel, 6-line wrasse, an emerald and mystery crab, and CUC so I don't think anything would hurt it if it was more exposed.

 

[mr_X]

I would leave it right where it is. It's most likely attached to the rock, so removing it might damage it. It's not photosynthetic, so you don't have to worry about putting it in the light.

 

[Petrichor]

Thanks for the information and advice! I wouldn't think about moving a clam physically in any case, but if he gets any bigger I might have to move the rock he's on so he can grow.